The invention concerns a method for the operation of gasification plants for pulverized fuels which, in particular, will raise the technical safety of such plants in cases of malfunctions.
In the technology of producing from solid fuels, synthesis gas, reduction gas, heating gas, and gas for public utilities, the gasification of pulverized fuels by partial oxidation, has shown to be an advantageous solution. With a method of this type, the pulverized fuel is reacted in a flame reaction, for instance, within a temperature range from 1200.degree. C. to 1600.degree. C. at normal or increased pressure, with a gaseous oxidizing agent containing free oxygen, called hereunder `gasifying agent`, wherein essentially CO and H.sub.2 will be generated. The reaction takes place in an empty reaction chamber, where average dwelling times in the hot reaction chamber, of the fuel and the gas resulting therefrom, will be of the magnitude of 0.5 s to 10 s. The gasifying agent is, as a rule, a mixture of technical oxygen and steam, wherein the content of technical oxygen will be between 60% and 95%, depending upon the fuel and the intended use of the gas.
Control of the method, in particular of maintaining optimal temperatures in the reaction chamber, is effected by controlling the ratio of technical oxygen to pulverized fuel, wherein deviations of 10% of the present value of the mass ratio of oxygen to fuel, may already lead to concomitant variations of the temperature within the reaction chamber by 200 K. When operating such a gasification plant, the danger exists that upon malfunctions in the fuel suppy especially upon an unintended reduction in the supply of the pulverized fuel, the temperatures within the reaction chamber will rise to such high values that the technical safety of the plant is questionable.
If the flow of pulverized fuel is reduced so far that the ratio of oxygen to fuel will exceed the stoichiometric amount required for complete combustion, or if the supply of pulverized fuel is fully interrupted, the oxygen, which is now present in excess, can react for a short while with the previously produced quantity of CO and H.sub.2 which is present within the hot reaction chamber. If the supply of oxygen is not securely shut off by the end of this phase, the temperature in the reaction chamber will drop again, however the danger remains of non-reacted free oxygen from the hot reaction chamber intruding into the subsequently arranged cooling and treatment apparatus for the produced gas, leading therein to the formation of explosive mixtures of oxygen and combustible hydrogen-containing gas and initiating severe explosions. To avoid such dangerous situations dust gasification plants of this type are equipped with an automatic emergency shut-off system which will securely close the oxygen supply and transfer the plant into a safe state, especially when the preset flow of pulverized fuel is not maintained, when the preset flow of oxygen is exceeded, and when the preset temperature range in the reaction chamber is either exceeded or not reached.
The automatic emergency shut-off will, because of the design, suffer a delay which is essentially determined by the delay in registering the measured values by the controls, and by the closing time of valves for the oxygen supply. With high capacity plants in particular, this closing time may be in the range of several seconds and may essentially determine the total delay. Despite the length of this closing time, sufficient safety against an oxygen discharge can be attained in case of a sudden interruption in the supply of pulverized fuel, if the ratio of the oxygen quantity flowing per time unit to the quantity of CO and H.sub.2 normally present in the reactor, can be made sufficiently small, and if provision is made for sufficient re-circulation within the reactor. Such a solution will, however, lead to low specific outputs of the reactor and thus to very large dimensions of the reactor. Another solution provides for sub-dividing the reaction chamber into several sections, which are operated largely independent of each other, each with its own supply system for fuel and gasifying agent, wherein, in case of a malfunction, any non-reacted oxygen that may in a given case be left in one of the sections, can react with gas produced in the other sections of the reaction chamber before a discharge into the cold parts of the plant could occur. This solution, too, is concatenated to increased expenditure for apparatus.
The objective of the invention is a method for the operation of gasification plants for pulverized fuels, which will preclude the danger of an oxygen discharge into the cooling and treatment plant for the produced gas, in case of malfunctions in the supply of pulverized fuel to the reactor, especially in case of a sudden interruption of this supply.